Leading a healthy lifestyle by eating well and exercising regularly can help prevent type 2 diabetes. But the disease can creep up on you without warning, so it's important to know your numbers to know if you are at risk and to improve your care.

The American Diabetes Association estimates about 7.2 million people 18 or older in the U.S. have type 2 diabetes but aren't aware of it. Even active people at normal weight can be at risk, especially if you have one or more of the following risk factors:

• High cholesterol levels.
  
  
• High blood pressure.
  
  
• A past or present smoking habit.
  
  
• A history of gestational diabetes (diabetes during pregnancy).
  
  
• Family history of heart disease, diabetes or both.

Your risk of diabetes increases as you get older. The risk is also higher for some racial and ethnic groups, including African-Americans, Mexican-Americans, Native Americans, Native Hawaiians, Pacific Islanders and Asian-Americans.

Experts recommend that you get tested for diabetes if you are:

• 45 or older.
  
  
• Between the ages of 19 and 44 and overweight or obese (based on BMI; see below), and you have one or more other diabetes risk factors.
  
  
• A woman who had gestational diabetes during pregnancy.

If your results are in a healthy range, you should continue getting tested every three years. Whether you're at risk or not, you should speak to your doctor if you notice any of the following symptoms:

• Frequent urination.
  
  
• Extreme thirst.
  
  
• Extreme hunger even though you are eating.
  
  
• Extreme fatigue.
  
  
• Blurry vision.
  
  
• Cuts or bruises that are slow to heal.
  
  
• Tingling, pain or numbness in your hands or feet.

Doctors use several tests to diagnose diabetes and may order tests a second time to confirm. These factors will help you understand your numbers and improve your care:

Body Mass Index (BMI)

BMI is not specifically for diabetes. It's a measure of your body's weight in relation to your height. Being overweight or obese increases your risk of diabetes. You can figure your BMI by plugging in your height and weight into a BMI calculator online. Here are the numbers to know:

• Underweight = less than 18.5.
  
  
• Normal weight = 18.5 to 24.9.
  
  
• Overweight = 25 to 29.9.
  
  
• Obese = BMI of 30 or greater.

BMI has its limitations. For example, it doesn't differentiate between weight due to muscle mass versus body fat. That said, your BMI can be a good starting point for learning about your health.

A1C Test

The A1C test measures your average blood glucose (blood sugar) over the past three months. This test requires you to give blood, but you won't have to fast (stop eating for a period of time) or drink a glucose tolerance drink, as with other diabetes tests. The A1C test looks at the attachment of glucose to hemoglobin, which is the protein in red blood cells that carries oxygen. Red blood cells usually live for about three months.

The A1C test gives you a percentage. The higher the percentage, the higher your blood sugar. Diabetes is diagnosed at 6.5 percent or higher. Results between 5.7 and 6.4 percent indicate prediabetes. Below 5.6 percent is considered a healthy A1C.

The A1C test does not always diagnose diabetes accurately, which is why you might need to have two types of tests. People who are more at risk of an inaccurate test result include those who:

• Are of African, Mediterranean or Southeast Asian descent.
  
  
• Have family members who have sickle cell anemia, a genetic blood disorder that limits red blood cell production.
  
  
• Have family members who have a thalassemia, a genetic blood disorder that creates abnormal hemoglobin.

What's more, test results can be outside of normal ranges in people who have anemia, heavy bleeding, liver disease or kidney failure.

Fasting Plasma Glucose (FPG) Test

The FPG test requires you to fast for at least eight hours before the test, meaning you can't eat or drink anything except water in that time. Because of this, you will usually be tested in the morning. Unlike the A1C test, the FPG test only measures blood sugar that is floating free in the blood at the time of the test. Diabetes is diagnosed if the test results are greater than or equal to 126 milligrams per deciliter.

Oral Glucose Tolerance Test (OGTT)

The OGTT measures how your body processes glucose. The test requires you to drink a medically prescribed sugary drink. Your blood sugar levels are tested before you consume the drink and again two hours after. Diabetes is diagnosed at greater than or equal to 200 mg/dL.

The OGTT is also used to test pregnant women for gestational diabetes, which is diabetes that develops during pregnancy.

Educating yourself about diabetes risk factors, symptoms and tests can help you know your numbers and lead a healthier life.